Excessive speed is being blamed for a fiery early-morning crash on the 401 that shut down eastbound lanes and left one man in critical condition.

Ontario Provincial Police said an SUV was travelling at high speeds just after 3 a.m. when the driver lost control and rear-ended a tractor trailer before slamming into a cement guard rail.

The SUV burst into flames and other motorists raced over to pull the driver from the burning vehicle.

OPP Constable David Woodford estimated the vehicle was travelling at approximately 150 kilometres per hour.

The 40-year-old driver from Oshawa remains in critical condition at Sunnybrook Medical Centre.

The tractor-trailer driver was not injured.

An off-duty Toronto police officer and an off-duty Toronto EMS supervisor are being touted as heroes for pulling the man from the wreckage.

"We dragged him about 40 feet to a safe distance away and then we started caring for the individual and then the vehicle burst right into flames. Fortunately, I think we got him out just in time," advanced care paramedic Glen Gillies said.

Both men were on their way home when they spotted the accident scene.

"He's still in critical condition but I would say he would have been dead at the scene if it hadn't have been for their actions," Woodford told CTV News.

Highway 401 eastbound lanes in Ajax were reopened at the Salem Road exit shortly after 9 a.m. on Tuesday.

"Everyone should be slowing down. It's out there in the press. I just shake my head at someone driving at a rate of speed like that," Const. Scott Hampsen, who rescued the man from the burning wreakage, said Tuesday.

With a report from CTV's Jim Junkin